This invention relates to an improved transport mechanism for feeding parts or articles serially along an axis without rotation. It is especially adapted for use with appropriate electro-optical apparatus for automatically and continuously inspecting cyclindrical or prismatic articles or parts, for example: shotgun shell bodies; bearing rollers; tubing; glass, metal, plastic, or paper containers; and the like. The improved transport mechanism permits the rapid inspection of such parts to detect not only local flaws and irregularities in their surfaces, but also geometric deviations from correct surface form, and incorrect part dimensions. Other applications include part counters, roll printers for labeling separate parts or continuous articles, and color examiners, among others.
The rate of automatic electro-optical inspection of parts has heretofore been limited in part by the mechanical limitations of the transport means available to feed the parts through an inspection zone at a high speed, yet with a precise orientation and location relative to the inspection apparatus. It has been proposed to simply drop parts for free fall through the inspection zone, but this only permits sorting the parts according to overall color, since their orientation and location varies in a random fashion as they pass through the inspection zone. To inspect for discrete surface flaws, it is necessary to locate the articles in the inspection zone with greater precision.
One known method for achieving this, which is used in conjunction with a non-rotating inspecting light beam, is to halt the longitudinal movement along a feed axis of each part as it arrives at a fixed location in the inspection zone, and to mechanically rotate the part while oscillating the inspecting beam back and forth in a plane parallel to the major axis of the part. This serves to inspect the entire surface of the part with a series of wave-form scans of the light beam. Such a system must either fully halt and damp any longitudinal movement and rebound of each part prior to its rotation and inspection, which severely restricts the rate of inspection of the parts; or it may permit continuous longitudinal motion of the parts if a tracking system is provided to compensate for this motion, which is complex and relatively expensive. Furthermore, the method is, so far as I am aware, limited to the detection of local flaws and irregularities, and does not lend itself to inspection of the diameters of the parts or their trueness to correct overall geometric form. If, for example, a part is not truly cylindrical, but is slightly curved in the axial direction (commonly referred to as a "banana"), or has an oval cross-section, this will not influence the reflection of the longitudinally-scanning light beam in any reliably-detectable degree. It would be necessary to examine the specific profile of the part in a separate operation using other known inspection apparatus, to detect defects of this nature.
A variation of the foregoing known method entails automatically loading the parts on a rotary conveyor whose axis of rotation extends parallel to the major axes of the parts, and which conveys the parts serially to an inspection station. This requires either that the conveyor be indexed step-wise, and halted as each part is rotated on its arrival at the inspection station, which results in a relatively limited rate of inspection; or that a complex tracking system be provided to compensate for continuous conveyor motion.
Another known approach is to mechanically feed the parts in a vertical direction downwardly past a stationary light beam, and to rotate them simultaneously by means of feed rollers tangential to the feed passage and rotating on axes inclined with respect to its longitudinal axis. While this method avoids the necessity to stop the motion of the parts, the inspection rate is limited by a different factor. The stationary beam sweeps out a helical path over the surfaces of the parts, and the rate of rotation must be fast enough relative to the rate of vertical feed to give this helical path a small axial pitch, as otherwise the successive circumferential sweeps of the light beam will be speced too far apart to permit a thorough inspection of the parts. But the rate of rotation must in actual practice be kept moderate to avoid excessive perturbation of the parts laterally of the feed axis; and the feed rate is accordingly limited.